Overload protection means for piezo-electric crystals



1933- F. MICHELSSEN 1,920,655

OVERLOAD PROTECTION MEANS FOR PIEZO ELECTRIC CRYSTALS Filed May 24. 1928INVENTOR $2 MICHELSSEN BY A ORNEY Patented Aug. 1, 1933 UNITED STATESPATENT OFFICE OVERLOAD PROTECTION MEANS FOR PIEZO-ELECTRIC CRYSTALS tionof Germany Application May 24, 1928, Serial No. 280,206, and

in Germany 5 Claims.

The present invention relates to a device for protecting piezo-electriccrystals whereby the chances of undue vibration of the crystal with theconsequent destruction thereof is automatically prevented. This isobtained by connecting a socalled limiting tube in series with thecrystal.

It has been found in practice that in case of a sudden increase inenergy of the transmitter comprising a quartz crystal coupled therewiththe crystal becomes overloaded and bursts. By the insertion of anelectronic tube of proper dimensions, that is, of appropriate saturationcurrent, in series with the crystal a simple means adapted to precludeoverloading, is furnished, the electron tube serving as a limitingdevice. If with such an apparatus, in the presence of a certaintransmitter energy, the coupling is so set that the tube is operating atits saturation point, then, in case of suddenly increased transmitterenergy, no larger load can be imparted to the crystal.

The accompanying drawing illustrates one embodiment of the basic ideahere disclosed by way of example.

S denotes the transmitter which is to be coupled with the quartzcrystal 1. The glow-discharge lamp 2 is connected in series therewith toindicate resonance. The coupling takes place by way of the limiting tube3 in the manner indicated in the drawing.

That is, the amount of energy transferred from transmitter S to crystal1 should be limited by the saturation of tube 3 so that crystal 1 willnot be in danger of over-energization.

This scheme, of course, is not confined to being applied tocrystal-controlled tube transmitters or transmitter valves, but will befound useful also in all such cases where the crystals are employed forwave measurement, for instance, for crystals with a rectifier tube ordetector connected therewith.

The present invention, of course, is particularly suited as a frequencyindicator, indicating when the source S corresponds in frequency to thefrequency of the piezo-electric crystal 1, although it is to be clearlyunderstood, of course, that this invention is not to be limited to thisparticular use.

I claim as my invention:

1. An arrangement to protect piezo-electric crystals from overloads,characterized by the feature that a limiting tube isconnectedeffectively in series with the crystal for radio frequencies appliedthereto which limiting tube is adjusted to become saturated uponpresence of excessive voltages, thereby limiting the voltage applied tothe crystal to a safe value.

June 25, 1927 2. A piezo-electric oscillating system comprising incombination, a source of radio frequency energy, a vacuum tube coupledto said source, and a piezo-electric crystal oscillator coupled to saidvacuum tube, said vacuum tube being adjusted normally to operate at itssaturation point, whereby to effect the energization of said crystal bysaid source.

3. A piezo-electric oscillating system comprising in combination, asource of alternating current energy, a vacuum tube coupled to saidsource, a piezo-electric crystal oscillator coupled to said vacuum tube,said vacuum tube being adjusted normally to operate at its saturationpoint, whereby to effect the energization of said crystal by saidsource, and a glow discharge lamp connected in series with saidpiezo-electric oscillator.-

l. In a system for undulatory electrical currents, a source ofundulatory electrical currents, an electron discharge device havingwithin an evacuated container, an anode, a cathode, and a grid, an inputcircuit coupled to said grid and cathode, means for coupling said sourceto said input circuit, an output circuit across said anode and cathode,a piezo-electric crystal coupled to said output circuit, and, a glowdischarge device associated with said crystal for indicating theapplication of potentials corresponding to a natural frequency ofvibration, to said crystals, said electron discharge device beingadjustedto become saturated upon the presence of excessive potentialsthereby preventing overloading of said piezo-electric crystal.

5. In a frequency indicating system, a source of undulatory electricalenergy, a piezo-electric crystal and a glow discharge device in series,and means for coupling said series combination to said source, saidmeans comprising an electron discharge device having an evacuatedcontainer wherein are contained an anode a cathode and a grid, theexcitation and polarization of the electrodes of said electron dischargedevice being such that application of energy of a value sufficient tobreak down said crystal is prevented by saturation of said electrondischarge device.

FRITZ MICHELSSEN.

